Method and apparatus for layer thickness control in additive manufacturing

ABSTRACT

An additive manufacturing apparatus is disclosed. The apparatus includes a build surface, at least a portion of which is transparent. The apparatus includes a first material depositor operable to deposit a curable resin to form a deposited resin layer on the build surface. A first sensing device is configured to measure the thickness of the deposited resin layer; and wherein the at least one sensing device is configured to generate a signal indicative of the thickness of the deposited resin layer. The first sensing device can be connected to a computer such that the additive manufacturing apparatus is configured to control the thickness of the deposited resin layer. The thickness of the deposited resin layer can be controlled such that it varies from side to side. The thickness can also be controlled such that it varies with time.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present specification is a division of U.S. application Ser. No.16/280,336 filed Feb. 20, 2019 and entitled “Method and Apparatus forLayer Thickness Control in Additive Manufacturing,” the entirety ofwhich is incorporated by reference herein.

BACKGROUND OF THE INVENTION

This invention relates generally to additive manufacturing, and moreparticularly to an apparatus and method for determining layer thicknessin additive manufacturing.

Additive manufacturing is a process in which material is built uplayer-by-layer to form a component. One prior art method is a tapecasting process. In this process, a resin is deposited as a layer havinga desired thickness onto a flexible radiotransparent tape that is fedout from a supply reel. An upper plate lowers onto the resin,compressing it between the tape and the upper plate and defining a layerthickness. Radiant energy is used to cure the resin through theradiotransparent tape. Once the curing of the first uncured layer iscomplete, the upper plate is retracted upwards, taking the curedmaterial with it. The tape is then advanced to expose a fresh cleansection, ready for additional resin to be deposited in a subsequent, newcycle.

Another prior art method employs a vat of liquid radiant-energy curablephotopolymer “resin” and a curing energy source such as a laser.Similarly, DLP 3D printing employs a two-dimensional image projector tobuild components one layer at a time. For each layer, the projectorflashes a radiation image of the cross-section of the component on thesurface of the liquid or through a transparent object which defines aconstrained surface of the resin. Exposure to the radiation cures andsolidifies the pattern in the resin and joins it to a previously-curedlayer. Other types of additive manufacturing processes utilize othertypes of radiant energy sources to solidify patterns in resin.

One problem with conventional methods of additive manufacturing is thatthe actual thickness of the deposited layer can vary both within a givenlayer of a given cycle and from cycle to cycle relative to an actualthickness. Such variation in the thickness of the deposited layer ofadditive manufacturing material, or resin, can result in a variety ofproblems and defects.

Another problem with conventional methods of additive manufacturing isthat photopolymer cure in response to light or radiation and thepenetration depth of the light or radiation into the resin is oftengreater than the desired layer thickness. In some cases, the penetrationdepth (Dp) can be 5 to 10 times greater than the desired layerthickness. Cured or partially cured resin transmits more light orradiation than uncured resin. This often results in a phenomenon knownas “print-through” in which light penetrates through existing featuresto unintentionally and undesirably cure resin. Print-through makes thecreation of thin internal structures difficult. These internalstructures define at least partial voids and can be overhangs, channelwalls, ribs, and other geometric features.

Conventionally, print-through is addressed by a technique known as “Zcompensation”. Z compensation involves carefully controlling layerthickness, curing energy (and therefore cured depth), and intentionallyomitting printing specific layers. The steps are done in anticipationthat print-through from later layers will occur and thus create thedesired cured geometry. However, Z-compensation does not provide forprecise control of individual layers and can result in manufacturinginefficiencies.

BRIEF DESCRIPTION OF THE INVENTION

At least one of these problems is addressed by an additive manufacturingapparatus configured to deposit resin for additive manufacturing to forma deposited layer in which the thickness of the deposited layer ismonitored. Methods are also provided for closed-loop control of thethickness of the deposited layer across the width of the layer and alongthe length of the layer.

According to one aspect of the technology described herein, an additivemanufacturing apparatus includes a build surface, at least a portion ofwhich is transparent. The apparatus includes a first material depositoroperable to deposit a curable resin to form a deposited resin layer onthe build surface. A first sensing device is configured to measure thethickness of the deposited resin layer; and wherein the at least onesensing device is configured to generate a signal indicative of thethickness of the deposited resin layer. The first sensing device can beconnected to a computer such that the additive manufacturing apparatusis configured to control the thickness of the deposited resin layer. Thethickness of the deposited resin layer can be controlled such that itvaries from side to side, i.e. across the width of the deposited resinlayer in the transverse direction along the x-axis. The thickness canalso be controlled such that it varies with time. Stated another way,the thickness can be controlled such that it varies in the machinedirection along the y-axis.

According to another aspect of the technology described herein, a methodfor producing a component layer-by-layer using an additive manufacturingapparatus includes the steps of maintaining the thickness of a layer ofresin for additive manufacturing at a predetermined thickness by thefollowing steps: using a first material depositor to deposit a curableresin to form a deposited resin layer on a build surface, at least aportion of which is transparent; sensing the thickness of the depositedresin layer; adjusting the thickness of the deposited resin layer todefine a region of the deposited layer that has a predeterminedthickness; and positioning the region of the deposited layer having apredetermined thickness in a build zone. The method then includes thestep of executing a build cycle, and this step includes the steps of:positioning a stage relative to the build surface so as to define alayer increment in the deposited resin layer having a predeterminedthickness; selectively curing the resin using an application of radiantenergy in a specific pattern so as to define the geometry of across-sectional layer of the component; moving the build surface and thestage relatively apart so as to separate the component from the buildsurface; introducing new resin into the build zone; and repeating thesteps of maintaining the thickness and executing the build cycle for aplurality of layers until the component is complete.

According to yet another aspect of the technology disclosed herein, amethod for using an apparatus for additive manufacturing to produce athree dimensional part that includes a void includes the followingsteps: A) depositing an uncured layer of resin that defines a resinsurface and a resin base that are spaced apart a thickness and whereinthe uncured layer of resin includes multiple thicknesses such that afirst uncured layer profile is defined; and B) curing the layer of resinto create a build layer that is a component of the part. The build layerhas a build layer profile that defines at least a portion of the void.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawing figuresin which:

FIG. 1 is a schematic side elevation view of an exemplary tape castingadditive manufacturing apparatus that includes a material depositor;

FIG. 2 is a schematic view of one embodiment of the material depositorshown in FIG. 1 ;

FIG. 3 shows a stylized representation of the initial relative positionsof a stage and platform in an additive manufacturing apparatus;

FIG. 4 shows a further relative position of the stage and platform inFIG. 3 ;

FIG. 5 shows a further relative position of the stage and platform inFIG. 3 ;

FIG. 6 shows a stylized representation of a failure mode;

FIG. 7 shows a stylized representation of a failure mode;

FIG. 8 shows a stylized representation of a failure mode;

FIG. 9 is schematic view of the material depositor of FIG. 1 thatincludes an additional sensor;

FIG. 10 is schematic view of the material depositor of FIG. 1 thatincludes two sensors and two control mechanisms;

FIG. 11 is a schematic view of a material depositor according to anotherembodiment being configured for side-to-side thickness control of adeposited layer;

FIG. 12 is schematic view of the material depositor of FIG. 1 beingconfigured for side-to-side thickness control of a deposited layerutilizing one sensor;

FIG. 13 is a schematic view of a material depositor;

FIG. 14 is a schematic side elevation view of an exemplary vat-typeadditive manufacturing apparatus that includes a material depositorillustrating material being deposited in a vat;

FIG. 15 is a view of the apparatus of FIG. 14 , showing a suction devicepositioned to remove material after overfilling of a vat;

FIG. 16 shows a layer of resin being further defined by contact with astage;

FIG. 17 is a view of the apparatus of FIG. 15 showing an alternativecuring mechanism;

FIG. 18 shows a configuration of the apparatus of FIG. 1 in which threematerial depositors are positioned side by side to define threespaced-apart lanes;

FIG. 19 shows a cross-section of three spaced-apart deposited layers ofresin supplied by the configuration of the apparatus shown in FIG. 18taken along line 19-19;

FIG. 20 shows an alternative embodiment that is configured to definethree contiguous lanes of deposited resin;

FIG. 21 shows another alternative embodiment that is configured todefine three contiguous lanes of deposited resin;

FIG. 22 shows a cross-section of a deposited layer of resin indicatingone possible profile;

FIG. 23 shows a cross-section of a deposited layer of resin indicatinganother possible profile;

FIG. 24 shows a cross-section of a deposited layer of resin indicatinganother possible profile;

FIG. 25 shows a cross-section of a deposited layer of resin indicatinganother possible profile;

FIG. 26 shows a cross-section of a deposited layer of resin indicatinganother possible profile;

FIG. 27 shows the deposited layer of resin shown in FIG. 26 in contactwith a working process part prior to curing of the deposited layeraccording to one disclosed method;

FIG. 28 shows a perspective view of an in-process part made according tothe method disclosed herein showing individual cured layers; and

FIG. 29 shows a perspective view of a finished part made according tothe method disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 illustratesschematically an example of one type of suitable apparatus 10 foradditive manufacturing with improved layer control. Apparatus 10utilizes a resin handling assembly 11 which, according to theillustrated embodiment, is a tape casting device 20. Resin handlingassembly 11 is suitable for and benefits from the use of a device formeasuring thickness of the deposited layer of resin. It should beappreciated that resin handling assembly 11 is an apparatus configuredfor a single-layer process. As described herein, tape casting is asingle-layer process. As described herein, the use of a plate as a resinsubstrate in lieu of a tape (i.e. “plate casting”) is also asingle-layer process. For vat processing, a single-layer process can beperformed when a vat is filled only to a depth that provides a singlelayer of resin or when the part is positioned relative to the vat anduncured resin to define a single layer of resin.

Referring to FIGS. 3-8 , the disclosed technology is suitable forreducing the number and magnitude of errors and imprecise layerdevelopment that occur with conventional additive manufacturingapparatuses and methods. As will be described in further detail below,but is being described here in order to detail the errors that thedisclosed technology address, an additive manufacturing apparatusincludes a stage 14. Referring now to FIG. 3 , the stage 14 defines asurface 30 on which a part 74 is formed. When referring to tape castingdevice 20, the machine direction, i.e., the direction a film 12 travels,is indicated as Y; the transverse direction is indicated as X; and thevertical direction is indicated as Z.

The part 74 defines a surface 75 on which a new layer of the part isadded by transfer of a cured portion of a layer 110 of resin positionedadjacent the surface 75 and supported by the film 12 (described in moredetail below). The layer 110 defines a surface 77. As shown in FIG. 4 ,error-free operation involves a predetermined amount of contact betweenthe surface 75 and the surface 77. The predetermined amount of contactresults in transfer of a cured portion of the layer 110 to form a newlayer of the part 74 and defines a new surface 75. A new portion oflayer 110 is moved below the part 74 to define a new surface 77. Thisconfiguration is shown in FIG. 5 .

There are at least two types of errors that are typical when consideringthe formation of a single layer. As illustrated in FIG. 6 , the layer110 is not thick enough to allow the surface 77 to contact the surface75 when the stage 14 and the part 74 are moved into a build positionappropriate for the existing geometry of the part 74. In this case, thecured portion of the layer 110 does not transfer to the part 74. In asecond error condition, shown in FIG. 7 , the layer 110 is too thicksuch that when the stage 14 and the part 74 are moved into a buildposition appropriate for the existing geometry of the part 74, thesurface 75 actually penetrates the surface 77 causing malformation ofthe part and potentially also damaging the part.

There are at least three types of errors that are typical whenconsidering layer-based errors that influence the formation of an entirepart. In a third error condition, also shown in FIG. 6 , errors in thethickness of previous layers 110 have resulted in a series of layers ofpart 74, some or all of which are too thin. Thus, the part 74 is not astall as expected. Thus, when the stage 14 is moved into a build positionthat is appropriate for the expected geometry, the surface 75 does notcontact the material layer 110 if the thickness of material layer 110 isas thick as expected or thinner. In a fourth error condition, also shownin FIG. 7 , errors in the thickness of previous layers 100 have resultedin a series of layers, some or all of which are too thick. Thus, thepart 74 is taller than expected such that when the stage 14 is movedinto a build position that is appropriate for the expected geometry, thesurface 75 penetrates the surface 77 causing malformation of or damageto the part. In a fifth error condition, shown in FIG. 8 , errors inthickness of previous layers 100 have resulted in a part 74 that is muchtaller than expected. Thus, when the stage 14 is moved into a buildposition, the stage 14 is lowered so far such that it “crashes” into thelayer 110, damaging the part. It can also push the part 74 through thematerial layer 110 to contact the film 12 or even to push through thefilm 12 to damage the machine. As shown in FIG. 8 , the film 12 hascontacted the part 74 with such force that the film 12 has beenseparated in several locations resulting in a web breakage or break-out.The disclosed technology addresses these errors by providing anapparatus and method for accurately defining the thickness of the layer110 to enable the part 74 to be constructed correctly.

It will be understood that configurations of the equipment other thantape casting can be used in apparatus 10 and can carry out a methoddescribed below. Those other configurations include different types ofresin handling equipment such as vats and/or plates. The method isadaptable for use with lower viscosity resins, slurries, and pastes, aswell as higher viscosity resins and/or powders. It will be understoodthat other configurations of equipment may be used to carry out themethod. Basic components of the exemplary apparatus 10 include amaterial depositing device 106 and a resin handling assembly 11, whichin FIG. 1 is a tape casting apparatus 20. The tape casting apparatus 20includes a support film or tape 12, and a radiant energy apparatus 18.

The tape casting apparatus 20 includes spaced apart rollers 15 with theflexible polymeric tape or foil 12 extending therebetween. A portion ofthe foil 12 is supported from underneath by a support plate 190.Suitable mechanical supports (frames, brackets, etc.—not shown) would beprovided for the rollers 15 and support plate 190. The foil 12 is anexample of a “resin support”.

Both of the support plate 190 and the foil 12 are transparent or includea portion or portions that are transparent. As used herein, the term“transparent” refers to a material which allows radiant energy of aselected wavelength to pass through. For example, as described below,the radiant energy used for curing could be ultraviolet light or laserlight in the visible spectrum. Non-limiting examples of transparentmaterials include polymers, glass, and crystalline minerals such assapphire or quartz.

Appropriate means such as motors, actuators, feedback sensors, and/orcontrols of a known type (not shown) would be provided for driving therollers 15 in such a manner so as to maintain the foil 12 tensionedbetween the rollers 15 and to wind the foil 12 from one of the rollers15 to another roller 15

The foil 12 extending between the rollers 15 defines a first “buildsurface” 24 which is shown as being planar, but could alternatively bearcuate (depending on the shape of the support plate). For purposes ofconvenient description, the first build surface 24 may be considered tobe oriented parallel to an X-Y plane of the apparatus 10. A directionperpendicular to the X-Y plane is denoted as a Z-direction (X, Y, and Zbeing three mutually perpendicular directions).

The first build surface 24 may be configured to be “non-stick”, that is,resistant to adhesion of cured resin. The non-stick properties may beembodied by a combination of variables such as the chemistry of the foil12, its surface finish, and/or applied coatings. In one example, apermanent or semi-permanent non-stick coating may be applied. Onenon-limiting example of a suitable coating is polytetrafluoroethylene(“PTFE”). In one example, all or a portion of the first build surface 24may incorporate a controlled roughness or surface texture (e.g.protrusions, dimples, grooves, ridges, etc.) with nonstick properties.In one example, the foil 12 may be made in whole or in part from anoxygen-permeable material.

Some means are provided for applying or depositing resin R to the firstbuild surface 24 in a generally uniform layer. FIG. 1 showsschematically the material depositor 106 configured for this purpose. Asshown in FIG. 2 , the material depositor 106 includes a reservoir 182.The reservoir 182 includes an upstream wall 194 and downstream wall 196and sidewalls 192. The upstream wall 194 has a slot 200 defined thereinto receive the foil 12. The downstream wall 196 defines an aperture orslot 202 that serves as an outlet for the foil 12 and the layer 110 ofresin R.

Continuing to refer to FIG. 2 , material depositor 106 includes a firstdoctor blade 210 and a second doctor blade 211 that are used to controlthe thickness of resin R applied to the foil 12, as the foil 12 passesunder the material depositor 106. According to the illustratedembodiment, the thickness of layer 110 is determined by doctor blades.By way of example and not limitation, other material depositingapparatus can be used separately or in combination with the first andsecond doctor blades 210 and 211 such as: gravure rolls, metering rolls,weir-based cascades, direct die casting, and a combination thereof. Thefirst doctor blade 210 is configured to act as a gross control for thethickness 213 of an initial deposited layer 215. There is provided anadjustment device 212 configured to adjust an angle 216 defined by asurface of the blade 210 and the top edge of wall 192. The greater theangle 216, the lower thickness 213, i.e., the thinner initial depositedlayer 215 will be. The adjustment device 212 can be a threaded screwassembly configured to extend and retract the order to affect change inthe angle 216. Adjustment device 212 is mechanically linked to the firstdoctor blade 210.

The second doctor blade 211 is movingly mechanically linked to thedownstream wall 196 and can be moved by an actuator 220 to adjust anddefine the outlet gap 202. A control signal as conventionally known isutilized to controllably connect the actuator 220 with the controller120. The layer 110 has a thickness 214 that is the distance between thesurface of the resin and the base of layer 110 which is in contact withthe surface of the foil 12. Accordingly, the thickness 214 of thematerial layer 110 can be adjusted by a control action such as movementof the doctor blade 211 in response to signals from the controller 120.By way of example and not limitation, suitable control signals can beone of the following: electrical, pneumatic, sonic, electromagnetic, anda combination thereof. By way of example and not limitation, othersuitable control actions include: varying the speed of the film 12,adjusting the viscosity or other rheological property of the resin R,changing the width of the deposited material layer 110 such as by therepositioning of side dams (not shown).

Continuing to refer to a FIG. 2 , a first sensor 224 is positioneddownstream of the second doctor blade 211. The first sensor 224 isconfigured to determine a thickness 214 of the deposited material layer110. As a result, the deposited material layer 110 has the thickness 214as it passes from the material depositor 106 into and through a buildzone 23 as shown in FIG. 1 . As represented in FIG. 2 , the first sensor224 is configured to generate monitoring signals indicative of thethickness 214 of the deposited material layer 110 and to transmit suchsignals to the controller 120. By way of example and not limitation,suitable monitoring signals can be one of the following: electrical,pneumatic, sonic, electromagnetic, and a combination thereof.

The controller 120 is configured to receive the monitoring signals andprocess such signals using predetermined algorithms to generate thecontrol signal discussed above that is subsequently transmitted to thecontroller 220. In this manner, closed loop control of the thickness 214of the deposited material layer 110 can be achieved according to themethod described below. It should be appreciated that the sensor 224, asillustrated in FIG. 2 , is configured to measure the thickness of asingle point in the deposited material layer 110. Because the depositedmaterial layer 110 has a width, variations in thickness across the widthwill not be detected by the sensor 224. Circumstances in which thethickness of the deposited material layer 110 varies across its widthare addressed by an embodiment described further below.

Optionally with regards to the method below, when the sensor indicatesthat the layer 110 is too thin additional resin R can be added toincrease the thickness of the layer 110. The additional material can beadded via a second depositor (not shown) positioned downstream of thedepositor 106. Further optionally, a thin layer 110 can be passedunderneath the depositor 106 a second time for additional resin R to beadded.

Referring again to components of the apparatus 10 (which are configuredto cure and define layers), the stage 14 is a structure defining theplanar surface 30 which is capable of being oriented parallel to thebuild surface 24 of the portion of the film 12 positioned over thesupport plate 190. Some means are provided for moving the stage 14relative to the build surface 24, parallel to the Z-direction. In FIG. 1, these means are depicted schematically as a simple actuator 32connected between the stage 14 and a stationary support structure 34,with the understanding that devices such as pneumatic cylinders,hydraulic cylinders, ball screw electric actuators, linear electricactuators, or delta drives may be used for this purpose. In addition to,or as an alternative to, making the stage 14 movable, the foil 12 and/orthe support plate 190 could be movable parallel to the Z-direction.

The radiant energy apparatus 18 may comprise any device or combinationof devices operable to generate and project radiant energy on the resinR in a suitable pattern and with a suitable energy level and otheroperating characteristics to cure the resin R during the build process,described in more detail below.

In one exemplary embodiment as shown in FIG. 1 , the radiant energyapparatus 18 may comprise a “projector” 48, used herein generally torefer to any device operable to generate a radiant energy patternedimage of suitable energy level and other operating characteristics tocure the resin R. As used herein, the term “patterned image” refers to aprojection of radiant energy comprising an array of individual pixels.Non-limiting examples of patterned imaged devices include a DLPprojector or another digital micro-mirror device, a 2D array of LEDs, a2D array of lasers, or optically addressed light valves. In theillustrated example, the projector 48 comprises a radiant energy source50 such as a UV lamp, an image forming apparatus 52 operable to receivea source beam 54 from the radiant energy source 50 and generate apatterned image 59 to be projected onto the surface of the resin R, andoptionally focusing optics 58, such as one or more lenses.

The radiant energy source 50 may comprise any device operable togenerate a beam of suitable energy level and frequency characteristicsto cure the resin R. In the illustrated example, the radiant energysource 50 comprises a UV flash lamp.

The image forming apparatus 52 may include one or more mirrors, prisms,and/or lenses and is provided with suitable actuators, and arranged sothat the source beam 54 from the radiant energy source 50 can betransformed into a pixelated image in an X-Y plane coincident with thesurface of the resin R. In the illustrated example, the image formingapparatus 52 may be a digital micro-mirror device. For example, theprojector 48 may be a commercially-available Digital Light Processing(“DLP”) projector.

As an option, the projector 48 may incorporate additional means such asactuators, mirrors, etc. configured to selectively move the imageforming apparatus 52 or other part of the projector 48, with the effectof rastering or shifting the location of the patterned image 59 of thebuild surface 24. Stated another way, the patterned image may be movedaway from a nominal or starting location. This permits a single imageforming apparatus 52 to cover a larger build area, for example. Meansfor mastering or shifting the patterned image from the image formingapparatus 52 are commercially available. This type of image projectionmay be referred to herein as a “tiled image”.

In another exemplary embodiment (as shown in FIG. 17 in relation to avat based resin transport system discussed further below), in additionto other types of radiant energy devices, the radiant energy apparatus18 may comprise a “scanned beam apparatus” 60 used herein to refergenerally to any device operable to generate a radiant energy beam ofsuitable energy level and other operating characteristics to cure theresin R and to scan the beam over the surface of the resin R in adesired pattern. In the illustrated example, the scanned beam apparatus60 comprises a radiant energy source 62 and a beam steering apparatus64.

The radiant energy source 62 may comprise any device operable togenerate a beam of suitable power and other operating characteristics tocure the resin R. Non-limiting examples of suitable radiant energysources include lasers or electron beam guns.

The beam steering apparatus 64 may include one or more mirrors, prisms,and/or lenses and may be provided with suitable actuators, and arrangedso that a beam 66 from the radiant energy source 62 can be focused to adesired spot size and steered to a desired position in plane coincidentwith the surface of the resin R. The beam 66 may be referred to hereinas a “build beam”. Other types of scanned beam apparatus may be used.For example, scanned beam sources using multiple build beams are known,as are scanned beam sources in which the radiant energy source itself ismovable by way of one or more actuators.

The apparatus 10 may include a controller 68. The controller 68 in FIG.1 is a generalized representation of the hardware and software requiredto control the operation of the apparatus 10, the stage 14, the radiantenergy apparatus 18, the transport mechanism 20, the depositor 106, andthe various actuators described above. The controller 68 may beembodied, for example, by software running on one or more processorsembodied in one or more devices such as a programmable logic controller(“PLC”) or a microcomputer. Such processors may be coupled to sensorsand operating components, for example, through wired or wirelessconnections. The same processor or processors may be used to retrieveand analyze sensor data, for statistical analysis, and for feedbackcontrol. It should be appreciated, that in some embodiments the functionand capabilities of the controller 120 are implemented in the controller68.

Optionally, the components of the apparatus 10 may be surrounded by ahousing 70, which may be used to provide a shielding or inert gasatmosphere using gas ports 72. Optionally, pressure within the housing70 could be maintained at a desired level greater than or less thanatmospheric. Optionally, the housing 70 could be temperature and/orhumidity controlled. Optionally, ventilation of the housing 70 could becontrolled based on factors such as a time interval, temperature,humidity, and/or chemical species concentration.

The resin R comprises a material which is radiant-energy curable andwhich is capable of adhering or binding together the filler (if used) inthe cured state. As used herein, the term “radiant-energy curable”refers to any material which solidifies in response to the applicationof radiant energy of a particular frequency and energy level. Forexample, the resin R may comprise a known type of photopolymer resincontaining photo-initiator compounds functioning to trigger apolymerization reaction, causing the resin to change from a liquid stateto a solid state. Alternatively, the resin R may comprise a materialwhich contains a solvent that may be evaporated out by the applicationof radiant energy. The uncured resin R may be provided in solid (e.g.granular) or liquid form including a paste or slurry.

According to the tape casting embodiment shown, the viscosity of theresin R is at a higher viscosity such that contact with a doctor bladeor a leveling device (such as the stage 14) is required. The compositionof the resin R may be selected as desired to suit a particularapplication. Mixtures of different compositions may be used.

The resin R may be selected to have the ability to out-gas or burn offduring further processing, such as the sintering process describedbelow.

The resin R may incorporate a filler. The filler may be pre-mixed withresin R. The filler comprises particles, which are conventionallydefined as “a very small bit of matter”. The filler may comprise anymaterial which is chemically and physically compatible with the selectedresin R. The particles may be regular or irregular in shape, may beuniform or non-uniform in size, and may have variable aspect ratios. Forexample, the particles may take the form of powder, of small spheres orgranules, or may be shaped like small rods or fibers.

The composition of the filler, including its chemistry andmicrostructure, may be selected as desired to suit a particularapplication. For example, the filler may be metallic, ceramic,polymeric, and/or organic. Other examples of potential fillers includediamond, silicon, and graphite. Mixtures of different compositions maybe used.

The filler may be “fusible”, meaning it is capable of consolidation intoa mass upon application of sufficient energy. For example, fusibility isa characteristic of many available powders including but not limited to:polymeric, ceramic, glass, and metallic.

The proportion of filler to resin R may be selected to suit a particularapplication. Generally, any amount of filler may be used so long as thecombined material is capable of flowing and being leveled and there issufficient resin R to hold together the particles of the filler in thecured state.

Examples of the operation of the apparatus 10 will now be described indetail with reference to FIGS. 1 and 2 . It will be understood that, asa precursor to producing a component and using the apparatus 10, thecomponent 74 is software modeled as a stack of planar layers arrayedalong the Z-axis. Depending on the type of curing method used, eachlayer may be divided into a grid of pixels. The actual component 74 maybe modeled and/or manufactured as a stack of dozens or hundreds oflayers. Suitable software modeling processes are known in the art.

The resin handling assembly 11 is operated to provide new resin R in thebuild zone 23. After the material is deposited, the apparatus 10 ispositioned to define a selected layer increment. The layer increment isdefined by some combination of the thickness of the deposited layer andthe operation of the stage 14. With regard to the tape casting system 20it would be the thickness 214 and the operation of the stage 14. For avat system (discussed below) it would be the depth in the vat to whichthe resin is filled. For example, the stage 14 could be positioned suchthat the upper surface 30 for new parts or the existing surface 75 forparts in process is just touching the applied resin R as shown in FIG. 2, or the stage 14 could be used to compress and displace the resin R topositively define the layer increment. The layer increment affects thespeed of the additive manufacturing process and the resolution of thecomponent 74. The layer increment can be variable, with a larger layerincrement being used to speed the process in portions of a component 74not requiring high accuracy, and a smaller layer increment being usedwhere higher accuracy is required, at the expense of process speed.

Once the resin R has been applied and the layer increment defined, theradiant energy apparatus 18 is used to cure a two-dimensionalcross-section or layer of the component 74 being built as shown in FIG.3 .

Where a projector 48 is used, the projector 48 projects a patternedimage 59 representative of the cross-section of the component 74 throughthe foil 12 to the resin R. This process is referred to herein as“selective” curing.

Once curing of the first uncured layer is complete, the stage 14 isseparated from the foil 12, for example by raising the stage 14 usingthe actuator 32. The technology disclosed herein provides a method andapparatus for measuring and controlling the thickness of the depositedmaterial, i.e. the layer 110.

Referring now to FIG. 2 , as the tape casting apparatus 20 is operated,the film 12 is advanced past the material depositor 106 toward andthrough the build zone 23. The resin R in the material depositor 106 isdragged, flows, or is pushed from the reservoir 198 and then from thereservoir 182 by the film 12. As the resin R is drawn from the reservoir198, it passes under the first doctor blade 210 and defines the initiallayer 215 having the thickness 213. The thickness 213 is determined bythe angle 216 of the first doctor blade 210. The dimensions of the firstdoctor blade 210 and its mechanical relationship to the reservoir 182are predetermined such that as the angle 216 approaches 90° thethickness 213 approaches a minimum. Correspondingly, as the angle 216decreases, i.e., becomes less than 90°, the thickness 213 increases andeventually approaches a maximum. The angle 216 is set using the actuator212. In the embodiment shown, this is a manual operation that isperformed relatively infrequently. The thickness 213 of the layer 215 ischosen such that the final thickness 214 can be achieved by adjustingthe position of the second doctor blade 211 to define the dimensions ofthe gap 202 and thus the thickness 214.

It should be appreciated that the actual relative positions of thesecond doctor blade 211 and the build surface 24 of the film 12 shouldcorrelate to the thickness 214. However, the thickness 214 might differfrom the height of the gap 202 due to various factors, including but notlimited to: the speed of the film 12; the rheological and mechanicalproperties of the resin R; the chemical properties and resultinginteractions between the resin R and the material that forms the film 12and the second doctor blade 211; and a combination thereof.

Continuing to refer to FIG. 2 , the sensor 224 operates to measure thethickness 214 and generates a measuring signal indicative of thethickness 214, and transmits it to the controller 120. The controller120 is configured to compare the thickness 214 as determined by thesensor 224, to a predetermined thickness value or “set point.” Ifnecessary, the controller 120 then generates a control signal thatactivates actuator 220 such that the position of the second doctor blade211 is changed relative to the reservoir 182; thus, changing thedimensions of the gap 202 and the thickness 214. The sampling rate ofthe sensor 224 and the rate of incremental actions by the controller 120are determined such that a stable and useful continuous control of thethickness 214 is maintained as the film 12 is moved between the rollers15. Thus, a region having a desired thickness is defined and the portionof the deposited material layer 110 in build zone 23 is maintained atthe desired thickness.

Referring now to FIG. 9 , there is shown an alternative configuration ofthe material depositor that includes a second sensor 225. The secondsensor 225 is configured to determine a thickness 180 of the layer 110.The second sensor 225 is also connected to the controller 120 and isconfigured similarly to the first sensor 224 such that the controller120 receives a second measuring signal from the second sensor 225 thatis indicative of the thickness at a point downstream of the first sensor224. As shown in FIG. 9 , the second sensor 225 is directly downstreamof, in series with, the first sensor 224. As such, the second sensorprovides additional data regarding the thickness of layer 110. Suchadditional data can be impacted by factors such as flow or self-levelingof layer 110 and or drying of layer 110. It should be appreciated thatthe data taken by the second sensor 225 for a given location is spacedapart in time from when data was taken for that given location by thefirst sensor 224 by a predetermined delay. The amount of the delay isdetermined by the distance the second sensor 225 is from the seconddoctor blade 211. For example, if the second sensor 255 is 2 metersdownstream from the doctor blade 211 and the film 12 is traveling at avelocity V of 1 meter per second, the delay is 2 seconds. During thistime, the thickness at the particular point could change due tosettling, flowing out, evaporation, or some other process. Thus, datafrom the second sensor 225 can be used to determine whether or notexpected processes such as settling out have occurred and to confirmthat the thickness is acceptable.

Further, the second measuring signal from the second sensor 225 canprovide data that is used in combination with data from the first sensor224, for example as an average. Alternatively, the second sensor 225 canbe controllingly coupled to a third doctor blade 217 via the controller120 in a cascading closed loop strategy, as illustrated in FIG. 10 .Alternatively or in addition, the data from sensor 225 can be used todetermine that intentional changes to the thickness of the materiallayer 110 (e.g. to construct a different portion of the part 74) havebeen properly executed (has the expected thickness) and that the newlayer thickness will reach the build zone 23 when expected.

Referring now to FIG. 11 , there is shown a configuration of materialdepositor 106 that includes multiple first sensors 224. As shown, suchmultiple first sensors 224 can be configured to provide averagethickness information across the width of the layer 110. Alternatively,each of the first sensors 224 can provide independent thicknessmeasuring signals. These independent signals can be used to determinevariation in the thickness 214 of the layer 110 across the width of thelayer 110. Such information can be used to control the thickness profileof the layer 110. For example, as shown, the multiple first sensors 224are positioned with one generally at a first point. In the illustratedembodiment, the first point is spaced away from a first side A alsoreferred to as the near side (in the foreground of FIG. 11 ), another ata second point that in the illustrated embodiment is generally at acenter of the width of the layer 110, and another at a third point that,in the illustrated embodiment, is generally spaced-away from a secondside B also referred to as an off side of the layer 110 (in thebackground of FIG. 11 ). The first, second and third points at which themultiple first sensors 224 are located define a line in the X ortransverse direction that is substantially perpendicular to the edges ofthe layer 110. The first, second, and third points are associated withfirst, second, and third thicknesses respectively. It is generallydesirable in additive manufacturing that the side-center-side profile ofthe layer 110 be flat. When the side-center-side profile is flat, thethickness 214 is consistent across the width of the layer 110 and thefirst, second and third thickness are generally equal. It should beappreciated that other profiles can be created utilizing materialdepositor 106. Examples of such profiles are shown in FIGS. 22-26 . Morespecifically, FIG. 22 shows a smile profile; FIG. 23 shows a skewedprofile which slopes from a thicker side in a generally straight line toa thinner side; FIG. 24 shows a frown or help profile; FIG. 25 shows atrough profile having two generally flat outside edges or lanes and agenerally flat central trough; FIG. 26 shows a modified trough profilewhere the outside edges have high centers. It should be appreciated thatother profile in other combinations of geometries can be producedutilizing depositor 106 or multiple depositors.

Referring now to FIGS. 11-13 , there is shown a configuration of thematerial depositor 106 that includes a sensor 524 that is configured toscan across the width of the layer 110. The sensor 524 is connected tothe controller 220 in the same manner as the first sensor 224 describedabove. The sensor 524 can be configured to provide average thicknessacross the width of layer 110 or a side-center-side thickness profile asdiscuss above in relation to the multiple first sensors 224 shown inFIG. 9 . Continuing to refer to FIGS. 11-13 , the material depositor canbe configured with a second actuator 199 that is controllably connectedto controller 120 in the same manner as actuator 220, described above.In this configuration, the first doctor blade 210 can be adjusted sideto side to control the side-center-side profile referred to above. Thefirst point can be controlled with regards to a first point targetthickness, i.e., setpoint, the center can be controlled with regards toa second target thickness, and the third point can be controlled to athird target thickness. For example, if the thickness of the layer 110measured at the first point by the associated first sensor 224 isgreater than the first target thickness, the actuator 199 can bemanipulated to make it thinner such that the measured thicknessapproaches the first side target thickness. It should be appreciatedthat all three target thicknesses can be different, the same, or otherpattern such as “toothed” where each target thickness is different andthree different general flat lanes are produced.

In another embodiment, the resin handling assembly 11 is a vat system.This embodiment is described, with relation to using vats 611, having afloor and walls to define a space which receives the resin. It should beappreciated that plates can be used in the system instead, so as toprovide a floor but not walls. Generally, the resin R should be flowablewhen used with a vat system and less flowable when plates are used.According to the embodiment shown in FIGS. 14-17 , the resin R ispreferably a relatively low viscosity liquid that is self-levelling. Theresin R can be a liquid having a higher viscosity such that contact withthe stage 14 is required to level the resin R.

A conveyor 21 is used to move a fresh vat 611 into the build zone 23. Amaterial depositor 56 operates to deposit resin R into the vat 611. Asensor 78 is provided to determine the thickness of the resin R in thevat 611. If the thickness of the resin R is not as much as required,controller 68 is configured to cause the material depositor 56 to addadditional resin R. If the thickness of resin R in vat 611 is too great,the controller 68 is configured to operate a suction device 57 to removeexcess resin R. These processes are repeated until the vat 611 isproperly filled with resin at a desired height, i.e., depth. For lessflowable (stiffer) resins, these processes are repeated until the vat611 is properly filled with resin at a desired height, i.e., depth, andis level (or flat) within a desired specification of flatness. In thismanner, a specified region, i.e., the area within the vat 611 ismeasured and corrected (material R removed or added) until the thicknessis correct. This is in contrast to the method indicated above whereincorrections are made to the layer 110 as it is being generated. Once aproperly filled vat 611 is positioned in the build zone 23, exposure tothe radiant energy selectively cures resin R as described above, andjoins the new layer to the previously-cured layer. This cycle ofpreparing a vat 611, incrementing a layer, selectively curing, andunloading the vat 611 is repeated until the entire component 74 iscomplete.

Referring now to FIG. 18 , there is shown an alternative configurationof the apparatus 10 which includes multiple depositors. In this regard,a first depositor 106; a second depositor 106′; and a third depositor106″ are positioned adjacent to each other over the film 12. Themultiple depositors are configured to deposit three spaced apart lanesof deposited material: a first lane 110, a second lane 110′, and a thirdlane 110″. As shown in FIG. 19 , all three lanes 110, 110′, and 110″have the same thickness. It should be appreciated that the three lanes110, 110′, and 110″ are of the same material, resin R, but optionallythe lanes 110, 110′, and 110″ can be formed of different materials.

Referring now to FIG. 20 , there is shown an alternative embodiment ofthe additive manufacturing apparatus 310 in which a first materialdepositor 306, a second material depositor 406, and a third materialdepositor 506 are provided. The first, second, and third materialdepositors 306, 406, and 506 are substantially similar to the material106 described above and can be understood from a description thereof.Each material depositor 306, 406, and 506 are configured to depositresin R onto a moving belt 312 at a predetermined thickness.Alternatively, each depositor 306, 406, and 506 can include a differentresin R and thus multiple materials can be used to build part 74.

As the belt 312 moves, the depositors 306, 406, and 506 operate todischarge resin R. In this manner, a first lane 308 having a first lanethickness, a second lane 408 having a second lane thickness, and a thirdlane 508 having a third lane thickness are produced. As shown in FIG. 20, lanes 308, 408, and 508 are touching and together define a layer 310.Optionally one or more of the lanes 308, 408, and 508 could be spacedapart. The spacing can be achieved by positioning the depositors 308,408, and 508 or by utilizing the depositors to control the width of thedeposited material. Thus, the spacing of the lanes 308, 408, and 508 canbe controlled over time.

In the embodiment shown in FIG. 20 , each of the three lanes aregenerally flat from side to side and the first lane thickness, thesecond lane thickness, and the third lane thickness are controlledrelative to the same setpoint such that all three thicknesses aresubstantially equal. It should be appreciated that the thickness oflanes 308, 408, and 508 can be different from each other such that allthree are different or one of the three are different from the othertwo. It should also be appreciated that the set points can be variedsuch that the thicknesses of lanes 308, 408, and 508 are varied overtime.

A follow-up thickness sensor 325 is positioned downstream of thedepositor 306 and is configured to measure the resin R thickness in thefirst lane 308 on the centerline 309 of the first lane 308. Thefollow-up thickness sensor 325 is configured to provide a signalindicative of thickness along the centerline 309 to the controller 68.The signal generated by the sensor 325 can be used to directly controlthe amount of material deposited by material depositor 306 or forconfirmation. The spacing of sensor 325 and the speed of the film 312downstream of the depositor 306 determines a predetermined time periodbetween the moment that the measured material was deposited and themoment of measurement. It should be appreciated that multiple follow-upsensors can be utilized across layer 310 or within any one or more ofthe lanes 308, 408, and 508. It should be appreciated that, as shown inFIG. 20 , the depositor 306, the depositor 406, and the depositor 506are positioned such that they each discharge resin at about the samelocation across the film 312.

As shown in FIG. 21 , in another alternative embodiment, there isprovided a depositor 706, a depositor 806, and they depositor 906. Thedepositors 706, 806, and 906 are configured to deposit layers 708, 808,and 908 respectively onto a film 712 and can be structurally andoperationally understood from the description of the depositors 306,406, and 506. It should be appreciated that the depositor 706 isconfigured to deposit resin that comprises a lane 708 further upstreami.e. earlier than a lane 808. Further, depositor 806 is configured todeposit resin that comprises the lane 808 further upstream i.e. earlierthan lane 908. Such spacing of the depositors 706, 806, and 906 canallow for accommodations of mechanical structures associated withadjacent depositors. Such spacing can also allow for accommodations ofmechanical and rheological properties of resin R in adjacent lanes 708,808, and 908. Again, it should be appreciated that the adjacent lanes708, 808, and 908 can be comprised of the same resins or differentresins.

Referring now to FIGS. 26-29 , an alternative embodiment is providedthat is configured to create multiple thicknesses within a build layerto precisely create overhangs, internal voids, and other geometries.Such geometries are generally difficult to create using conventionalmeans of additive manufacturing due to the print-through phenomena.Accordingly, a method of manufacture for operating a 3D printerutilizing additive manufacturing with build styles that allow thecreation of multiple thicknesses within a layer is disclosed below.

Advantages of the disclosed method over methods of the prior art includeimproved production rates, the ability to create more fragile features,the ability to create voids, and greater precision. The disclosed methodshould provide layers that are created with the correct thickness suchthat the layers are cleaner and print-through does not occur becauseexcess resin is not deposited. Another advantage of the disclosed methodover the prior art is that the prior art often leaves the newly createdvoid full of uncured material. Any uncured material that is not orcannot be removed during an in-process or post-printing cleaning step iscured into the part (thus, partially or completely filling the void)during postprocessing. The disclosed method creates internal featureswith little or no entrapped uncured material or resin R and thereforecreates features that will survive postprocessing.

It should be noted that a feature of the present method is that all thelayers that are printed at the same time and have their base in the sameplane, i.e., on the surface 24 of film 12.

A part having voids defined within it can be produced according to thefollowing method. It should be appreciated that the voids can bechannels through the part that have open ends, enclosed cavities,partially enclosed cavities balance only on one or two sides, i.e.,overhangs, or other complex geometries.

Such parts can be created by stacking one or more layers having shapedor otherwise non-flat profiles. Such shaped layers can be interspersedwith conventional flat layers.

For example, the in-process part shown in perspective in FIG. 28 isformed of five U-shaped build layers 79 formed on an initial build layerhaving a generally uniform thickness. The in-process part 74 defines thefinished part 74″. It should be appreciated that optionally,conventional cleaning and finishing steps can be applied to thein-process part 74 to produce the finished part 74″.

Preferably, the in-process part 74 is formed utilizing a U-shaped layer310 being configured as shown in FIG. 25 with square outside lanes 308and 508. Such precisely deposited shaped layers allow for the formationof a part without print-through. Because the layer 310 shown in FIG. 25does not have excess resin, it is not possible to have print-througherrors. In other words, the profile of the layer 310 generally matchesthat of the resulting build layer of the finished part.

However, it should be appreciated that similar parts having cavitieswithin them can be formed utilizing stacked shaped layers where theprofile of the deposited layer does not match the finished build layershape. As indicated above, the stage 14 can be utilized to contact adeposited layer in such a way that the surface 30 of the stage 14contacts the deposited layer 110 and defines its uppermost surface. Forexample, FIG. 26 shows a shaped layer 710 having two outside ridges 708and 908. According to the present method, a shaped layer 710 can beutilized to make the part 74 shown in FIG. 28 . An initial step ofdefining the final uncured layer shape by moving the working surface 75to contact and deform the deposited uncured resin layer 710 as shown inFIG. 27 is provided. This step is utilized to approximate the preciselydeposited U-shaped channel shown in FIG. 25 .

In this regard, the uncured resin layer 710 of FIG. 26 includes agenerally flat center lane 808 bounded by peaked first and secondoutside lanes 708 and 908. The shape and size of the peaks of theoutside lanes 708 and 908 are chosen to comply with the build style andaccount for deformation of the outside lanes 708 and 908 by contact withthe surface 30 of the stage 14 to define an approximation of one of thedesired U-shaped layers as shown in FIG. 28 . Due to the mechanicaldeformation process required to shape the outside ridges 708, 908 itshould be appreciated that some uncured resin 79′ might be left withinthe channel 79. This uncured resin 79′ can be removed by variousconventional cleaning processes such as chemical flushing. Cleaningsteps can be conducted on the working process part 74 or as part of thefinishing processes to produce the finished part 74″ shown in FIG. 29 .While the step of mechanically deforming the deposited layer prior tocuring can produce the desired finished shape, it can also produce somewaste and possible print-through artifacts.

The alternative embodiment described above provides a method for usingan apparatus for additive manufacturing to produce a three-dimensionalpart that includes a void. As used herein, the term void refers to aspace within a build layer that is defined by an uncured resin layerthat has various thicknesses. In this regard, the uncured resin layerthat defines a build layer with a void has at least one “thinner”region. The method can be better understood from the listing of thesteps below: A) depositing an uncured layer of resin that defines aresin surface and a resin base that are spaced apart a thickness andwherein the uncured layer of resin includes multiple thicknesses suchthat a first uncured layer profile is defined; B) curing the layer ofresin to create a build layer that is a component of the part; C)wherein the build layer has a build layer profile that defines at leasta portion of the void; and D) repeating the depositing and curing stepsto create a part that includes multiple build layers and that includesthe void and the void has a predetermined geometry.

According to an alternative embodiment the following steps are providedto create a part having a void where the deposited layers are shaped bycontact with the mechanical shaper such as the stage 14. The steps ofthe alternative embodiment method are: E) contacting at least a portionof the resin surface with a working surface; F) changing the firstuncured layer profile to define a second uncured layer profile duringthe step of contacting; G) cleaning residual uncured resin from the partand H) removing undesired cured resin to define a final part shape.

The foregoing has described a method and apparatus for additivemanufacturing. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

What is claimed is:
 1. A method for using an apparatus for additivemanufacturing to produce a three dimensional part that includes a void,the method comprising the steps of: depositing an uncured layer of resinthat defines a resin surface and a resin base that are spaced apart athickness and wherein the uncured layer of resin includes multiplethicknesses such that a first uncured layer profile is defined; curingthe layer of resin to create a build layer that is a component of thepart; and wherein the build layer has a build layer profile that definesat least a portion of the void.
 2. The method of claim 1, wherein thefirst uncured layer profile is substantially the same as the build layerprofile.
 3. The method of claim 1, wherein dimensions of the build layerare defined by dimensions of the uncured resin layer produced by thedepositing step.
 4. The method of claim 1, further comprising the stepsof repeating the depositing and curing steps to create a part thatincludes multiple build layers and that includes the void and the voidhas a predetermined geometry.
 5. The method of claim 4, wherein thepredetermined geometry can include at least a portion of one of thefollowing: an overhang, an internal void, an internal void that includesa structure positioned therein, and a combination thereof.
 6. The methodof claim 1, wherein the uncured layer of resin is positioned such thatit has an x-axis, a y-axis, and a z-axis and the first profile isoriented generally perpendicular to the x-axis.
 7. The method of claim1, wherein the uncured layer of resin is positioned such that it has anx-axis, a y-axis, and a z-axis and the first profile is orientedgenerally perpendicular to the y-axis.
 8. The method of claim 1, furthercomprising the step of depositing the uncured layer of resin such thatmultiple lanes are defined within the uncured layer of resin.
 9. Themethod of claim 8, further comprising the step of depositing themultiple lanes such that at least two lanes have different thicknesses.10. The method of claim 8, further comprising the step of depositing themultiple lanes such that at least two lanes have substantially similarthicknesses.
 11. The method of claim 10, further comprising the step ofdepositing an additional lane between the two lanes that havesubstantially similar thicknesses such that the additional lane has adifferent thickness than within the thickness of the two lines that havesubstantially similar thicknesses.
 12. The method of claim 11, whereinthe additional lane is thinner than at least a portion of the two lanesthat have substantially similar thicknesses.
 13. The method of claim 1,further comprising the steps of contacting at least a portion of theresin surface with a working surface; and changing the first uncuredlayer profile to define a second uncured layer profile during the stepof contacting.
 14. The method of claim 13, wherein the second uncuredlayer profile is substantially the same as build layer profile.
 15. Themethod of claim 13, further comprising the step of cleaning residualuncured resin from the part.
 16. The method of claim 13, furthercomprising the step of removing undesired cured resin to define a finalpart shape.
 17. The method of claim 1, further comprising the step ofcuring by exposing different portions of the resin layer with differentamounts of radiation.
 18. The method of claim 1, further comprising thestep of repeating the depositing and curing steps to create at least oneadditional build layer that further defines the void.